1. Field of the Invention
The present invention relates to a device for recording a curing temperature history on precast concrete products, and more particularly to a device for recording a curing temperature history on precast concrete products, which is buried in a precast concrete product so as to record curing temperature and time histories during a steam curing procedure and to inform a user/inspector of recorded data, thereby controlling the quality of the steam curing concrete products.
2. Description of the Related Art
Generally, concrete curing refers to a procedure in which proper temperature and humidity (moisture) are imposed on concrete so as to achieve sufficient hardenability between a step of mixing concrete and another step of hardening concrete, or a procedure in which an exposed surface of concrete is protected from excessive impact or load, wind, rain, frost, light before the concrete is hardened so as to have a sufficient strength.
Concrete curing is generally divided into three methods, i.e., common curing, steam curing, and autoclave curing. Individual procedures of the above three curing methods will be described in detail as follows.
In the common curing procedure, concrete is pressed in a mold, and water is sprayed or a water-soaked straw bag or sawdust is covered over the concrete for 1 week so that the surface of the concrete is not dried, without the rise of temperature, thereby preventing lack of the strength of the concrete and cracks formed in the concrete due to drying shrinkage, and freezing of the concrete.
In the steam curing procedure, over several hours after the mixing of concrete, temperature and moisture are provided to the concrete via steam so as to have a proper strength at an initial stage. Generally, concrete products for use in road construction or precast concrete products are cured by this steam curing procedure. A concrete bench flume is a typical one of these concrete products manufactured by the steam curing procedure.
In the autoclave curing procedure, the compressive strength of the concrete is remarkably improved by fibrous crystals, which is a cement hydrate generated under a high-temperature and a high-pressure condition.
As shown in FIG. 1, at a factory, a concrete product is manufactured by acceleratedly curing concrete by means of steam of a high-temperature. First, non-hardened watery concrete fills a mold and is pressed using vibration or centrifugal force. Subsequently, the mold filled with the pressed concrete is transferred to a steam-curing chamber of a high temperature and then cured therein. The mold filled with the cured concrete is taken out of the curing chamber, and the cured concrete is separated from the mold. A plurality of the cured concretes are stacked and stored outdoors.
For example, in case that a bench flume 10 shown in FIG. 2 is manufactured, a mold 20 shown in FIG. 3 is prepared.
The non-hardened watery concrete fills the mold 20 and is pressed using vibration and centrifugal force. Then, the mold 20 filled with the pressed concrete is transferred to the steam-curing chamber of a high temperature and cured therein in a short period of time.
The mold 20 filled with the cured concrete is taken out from the steam-curing chamber, and the cured concrete is separated from the mold 20. Thereby, the concrete bench flume shown in FIG. 2 is obtained. The obtained bench flume are transferred outdoors and then piled.
When the bench flume is separated from the mold 20, connection means such as screws 22 for connecting a flange to a main body of the mold 20 are detached from the flange and the main body.
When the concrete is acceleratedly cured, as indicated by a dotted line in FIG. 10 (a curing pattern of concrete in accordance with the present invention), the concrete is maintained at a normal temperature for approximately 4 hours so that an initial hydration reaction is performed. Then, after the initial hydration reaction is completed, the concrete is transferred into the steam-curing chamber.
Here, steam is supplied into the steam-curing chamber, such that the temperature in the steam-curing chamber rises less than 20° C. per hour, thereby maximally being 65° C.
This maximum high temperature is maintained for approximately 6 hours, and then the supply of steam is controlled so that the temperature in the steam-curing chamber falls less than 20° C. per hour. Thereby, it is possible to improve the quality of an acceleratedly cured concrete product (i.e., a bench flume), thus lengthening the life time of the product.
In this case, it takes more than approximately 16 hours to perform one cycle of the steam curing procedure for manufacturing products, thus improving the production cost of the concrete product and reducing the productivity of the concrete product manufacturing process. Accordingly, it is difficult to actually use the above conventional steam curing procedure to mass-produce concrete products.
In order to solve the above problems, an actual manufacturer heats concrete at a temperature of more than 85° C.˜90° C. using a temporary expedient, thereby completing one cycle of a curing procedure within 5˜6 hours.
However, with this method, a time taken to expose concrete to steam of a high temperature is shorter than a time taken to set cement. Accordingly, non-hydrated cement is produced, thus reducing the quality of the resulting concrete product.
Further, since the maximum temperature is more than 85° C.˜90° C., the pore structure of the hydrate is weak and easily damaged by the freezing-thawing. Thus, fine cracks are excessively formed in the hydrate by thermal expansion and contractile force due to sudden change of the temperature.
In case that the fine cracks are formed in concrete, the obtained concrete product installed on a moist soil is easily damaged by the freezing-thawing. Thereby, the life cycle of the concrete product is remarkably shortened up to 7˜8 years.
The shortage of the life cycle of the concrete product causes the cost for installing another replacement concrete product. Further, since waste products must be disposed and raw material for producing additional product (aggregate and cement) is required, the shortage of the life cycle of the concrete product seriously destroys soil environment.